The present invention relates to an automatic overload protection system for a radio receiver and, more particularly, to such a system which is particularly adapted to protect the input circuitry of the receiving portion of a radio transceiver from damage or malfunction.
A radio system such as a transceiver and especially a portable transceiver is commonly used under circumstances where the intensity of an input signal to the receiver portion thereof varies considerably. To accommodate such signal strength variation, a circuit commonly referred to as an automatic gain control (AGC) circuit is typically employed. The AGC circuit varies the bias of the amplifying transistor(s) of the input stage(s) to increase the gain for weak input signals and decrease it for strong signals. If a relatively very high level signal is applied to the input, the AGC circuit will decrease the gain but the input circuitry (particularly the amplifying transistors) may still be damaged by the excessive power of the signal.
This situation can occur in any radio, of course, but it is especially likely in a radio transceiver when the transceiver is rapidly switched from the transmit mode to the receive mode. If the transmit circuitry remains active when the receive circuitry is activated, even if the overlap is only momentarily, the input circuitry of the receiver may be damaged by the overload because the conventional automatic gain control circuit provides inadequate protection of the receiver in that it does not harmlessly dissipate the excess energy.
It is therefore an object of the invention to provide a new and improved system for protecting the input of a radio circuit from damage or malfunction caused by excessively high input signals.
It is another object of the invention to provide such a system which is particularly adaptable to a radio transceiver.
It is yet another object of the invention to provide such a system which overcomes the inability of conventional AGC circuits to adequately protect an input circuit from excessively high, potentially damaging input signals.